This invention relates to a method and apparatus for stacking and, more particularly to one providing full count stacks independent of supply.
Means for accumulating products to take up the difference between the rate of input and the rate of discharge are well known in the art--see, for example U.S. Pat. No. 4,142,626. Accumulators such as that in the '626 patent are arranged with separately driven input means so that they will only rotate as a function of incoming product, and likewise, the discharge end of the accumulating device is separately driven by a motor that is slave to downstream equipment. Accumulators described heretofore operate with a continuously driven input as long as upstream equipment is operating, and with continuous discharge as long as downstream equipment is operating. In the event that either upstream or downstream equipment stops, the chain loop configuration is changed to accept the differential. Accumulating devices to accept a continuous series of products, or an intermittent series of products at the infeed end and discharge a continuous series or intermittent but consecutive series of products at the discharge end are well known, but the invention is believed to be unique because of the intermittent motion at the discharge end which results in the unique ability to discharge a plurality of products--for example a 12 count stack of product, and further resides in the ability of the accumulating device to remain full while culling products (interrupting product flow to infeed), and still retain the ability to advance a full count stack to the discharge area in one or more steps.
Exemplary of the application of the invention is the production of disposable diapers--normally packaged by the dozen. These are produced on continuously operating machines which deliver diapers serially along a horizontal path--complete with fastening tabs. From time to time, a defective diaper may be delivered which has to be culled from the line before packaging. In the past, when this occurred, A "short count" stack was sensed and automatically diverted to a second delivery zone where operators counted the shortage, added an equal number of good diapers to complete the stack, and then manually packaged the now completed stacks, or manually transfer them to the normal packaging infeed conveyor. Although salvage and manual handling of short count stacks is justified, it is nonetheless highly labor-intensive and often disruptive to the normal packaging operation, thus thwarting the object of a high speed, automatic production line. This is avoided by the invention which is particularly well suited for installations where space is minimal and the product stream is temporarily interrupted.
The invention achieves these heretofore unavailable benefits. By providing a closed loop accumulator, serially introducing a product at a first point in the loop while periodically removing a product stack adjacent a second point, expanding the upper portion of the loop between the first and second points while contracting the remaining portion--this being responsive to the introduction of the product. Thereafter when sufficient product has been accumulated, the upper portion is contracted for a period to position a predetermined count of product in position for removal. After periodic contraction, the stack is removed--this while the continued inflow of product causes expansion of the upper loop portion. The invention is embodied in apparatus which has four sprocket means arranged in quadrilateral fashion, two of which are translatable and two are fixed in space so that the expansion and contraction of the loop portion is efficiently achieved between the receiving and delivery points.
Other objects and advantages of the invention may be seen in the details of the ensuing specification.